SONAR is an acronym that stands for “Sound Navigation and Ranging” and is a technique that uses sound propagation under water to navigate or detect objects in or on the water. Sonar may be active, in which case a pulse of sound is emitted and then reflections of the pulse from objects are received, or sonar may be passive, in which case objects are detected by listening for sound emanating from such object. Thus, active sonar requires a transmitter and a receiver, while passive sonar requires only a receiver. While logically they are different devices with different functions, physically they can be the same device.
Passive sonar receivers may utilize arrays of sensors formed from piezoelectric crystals or ferroelectric ceramics. Each of the sensors in each array transforms the received acoustic signal into an electrical signal by converting pressure variations into a corresponding voltage variation. This type of receiver typically requires long copper wires or cables for each sensor in each array, adding significant weight and cost. Further, electromagnetic interference problems may arise without the use of the more expensive and heavier coaxial cable.
Passive sonar receivers may also rely on fiber optic-based sensors arranged in arrays. However, conventional fiber optic-based sensors require at least one fiber per sensor and require that each separate sensor be individually formed.
Accordingly, there is a need for a passive sonar receiver which overcomes the drawbacks recited above.